1. Field of the Invention
The present invention relates to an image recording material which can be used as a planographic printing plate, color proof, photoresist and color filter. More particularly, the present invention relates to a negative type image recording material suitably used as a planographic printing plate which is capable of directly producing a printing plate by scanning the printing plate using an infrared laser based on digital signals output from a computer or the like.
2. Description of the Related Art
Conventionally, as systems for making a printing plate directly from digital computer data, there have been proposed (1) a system using an electrophotographic method; (2) a system using a photopolymerizable compound, which polymerizes by being exposed to a laser which emits blue or green light; (3) a system using a recording material in which a silver salt is laminated on a photosensitive resin; and (4) a system using a silver salt diffusion transfer method.3
However, the system using an electrophotographic method (1) above has complicated image formation processes such as charging, exposure, developing, and the like and therefore the apparatus thereof becomes sophisticated and large. In a system using a photopolymerizable compound (2) above, since a printing plate which is highly sensitive to blue or green light is used, it is difficult to handle in an illuminated room. In methods (3) and (4), since a silver salt is used, there are the disadvantages that processes such as developing and the like become complicated and the waste solution naturally contains silver.
In recent years, laser technologies have developed remarkably. In particular, high output and compact solid-state lasers and semiconductor lasers emitting infrared rays of a wavelength of 760 nm to 1,200 nm are readily available. These lasers are very useful as a light source for recording in the direct production of a printing plate from digital computer data. However, since most practical useful photosensitive recording materials are sensitive to visible light having a wavelength of 760 nm or less, image recording cannot be carried out with these infrared lasers. Therefore, a material recordable with an infrared laser is desired
As an example of the image recording materials capable of recording images by the use of an infrared ray laser, a recording material comprising an onium salt, a phenol resin and a spectral sensitizing agent is disclosed in U.S. Pat. No. 4,708,925. However, the image recording material is a positive type recording material utilizing the dissolution prevention effect, generated by the onium salt and the phenol resin, with respect to the developer. On the other hand, examples of negative type image recording materials include a recording material comprising an onium salt, a resol resin, a novolak resin, and an infrared ray absorbing agent disclosed in U.S. Pat. No. 5,372,907. According to the image recording material, a positive image is obtained only with laser exposure, but by conducting a heat treatment after the laser exposure, a negative image can be obtained. In general, in order to obtain a negative image, coated layer should not remain on unexposed portions which are non-image portions, after developing. When the image recording material disclosed in U.S. Pat. No. 5,372,907 is heat treated after exposure under mild conditions, positive type characteristics By of the recording material become difficult to eliminate and coated layer tends to remain on the unexposed portions. Accordingly, a printing plate utilizing this type of image recording material suffers from the problem of staining at the time of printing. Furthermore, the printing plate using this type of image recording material lacks layer strength in the image portion and consequently printing durability at the time of printing is insufficient.